package com.gitee.yusugar.core.coder;

import javax.crypto.Cipher;
import java.security.*;
import java.security.interfaces.RSAPrivateKey;
import java.security.interfaces.RSAPublicKey;
import java.security.spec.PKCS8EncodedKeySpec;
import java.security.spec.X509EncodedKeySpec;
import java.util.HashMap;
import java.util.Map;


/**
 * 非对称加密算法RSA算法组件
 * 非对称算法一般是用来传送对称加密算法的密钥来使用的，相对于DH算法，RSA算法只需要一方构造密钥，不需要
 * 大费周章的构造各自本地的密钥对了。DH算法只能算法非对称算法的底层实现。而RSA算法算法实现起来较为简单
 *
 * @author Y-sugar
 */
public class RSACoder {
    // 非对称密钥算法
    private static final String KEY_ALGORITHM = "RSA";

    /**
     * 密钥长度，DH算法的默认密钥长度是1024
     * 密钥长度必须是64的倍数，在512到65536位之间
     */
    private static final int KEY_SIZE = 512;
    // 公钥
    private static final String PUBLIC_KEY = "RSAPublicKey";
    // 私钥
    private static final String PRIVATE_KEY = "RSAPrivateKey";

    /**
     * 初始化密钥对
     *
     * @return Map 甲方密钥的Map
     */
    public static Map<String, Object> initKey() throws Exception {
        //实例化密钥生成器
        KeyPairGenerator keyPairGenerator = KeyPairGenerator.getInstance( KEY_ALGORITHM );
        //初始化密钥生成器
        keyPairGenerator.initialize( KEY_SIZE );
        //生成密钥对
        KeyPair keyPair = keyPairGenerator.generateKeyPair();
        //甲方公钥
        RSAPublicKey publicKey = (RSAPublicKey) keyPair.getPublic();
        //甲方私钥
        RSAPrivateKey privateKey = (RSAPrivateKey) keyPair.getPrivate();
        //将密钥存储在map中
        Map<String, Object> keyMap = new HashMap<>();
        keyMap.put( PUBLIC_KEY, publicKey );
        keyMap.put( PRIVATE_KEY, privateKey );
        return keyMap;

    }

    /**
     * 私钥加密
     *
     * @param data 待加密数据
     * @param key  密钥
     * @return byte[] 加密数据
     */
    public static byte[] encryptByPrivateKey( byte[] data, byte[] key ) throws Exception {

        //取得私钥
        PKCS8EncodedKeySpec pkcs8KeySpec = new PKCS8EncodedKeySpec( key );
        KeyFactory keyFactory = KeyFactory.getInstance( KEY_ALGORITHM );
        //生成私钥
        PrivateKey privateKey = keyFactory.generatePrivate( pkcs8KeySpec );
        //数据加密
        Cipher cipher = Cipher.getInstance( keyFactory.getAlgorithm() );
        cipher.init( Cipher.ENCRYPT_MODE, privateKey );
        return cipher.doFinal( data );
    }

    /**
     * 公钥加密
     *
     * @param data 待加密数据
     * @param key  密钥
     * @return byte[] 加密数据
     */
    public static byte[] encryptByPublicKey( byte[] data, byte[] key ) throws Exception {

        //实例化密钥工厂
        KeyFactory keyFactory = KeyFactory.getInstance( KEY_ALGORITHM );
        //初始化公钥
        //密钥材料转换
        X509EncodedKeySpec x509KeySpec = new X509EncodedKeySpec( key );
        //产生公钥
        PublicKey pubKey = keyFactory.generatePublic( x509KeySpec );

        //数据加密
        Cipher cipher = Cipher.getInstance( keyFactory.getAlgorithm() );
        cipher.init( Cipher.ENCRYPT_MODE, pubKey );
        return cipher.doFinal( data );
    }

    /**
     * 私钥解密
     *
     * @param data 待解密数据
     * @param key  密钥
     * @return byte[] 解密数据
     */
    public static byte[] decryptByPrivateKey( byte[] data, byte[] key ) throws Exception {
        //取得私钥
        PKCS8EncodedKeySpec pkcs8KeySpec = new PKCS8EncodedKeySpec( key );
        KeyFactory keyFactory = KeyFactory.getInstance( KEY_ALGORITHM );
        //生成私钥
        PrivateKey privateKey = keyFactory.generatePrivate( pkcs8KeySpec );
        //数据解密
        Cipher cipher = Cipher.getInstance( keyFactory.getAlgorithm() );
        cipher.init( Cipher.DECRYPT_MODE, privateKey );
        return cipher.doFinal( data );
    }

    /**
     * 公钥解密
     *
     * @param data 待解密数据
     * @param key  密钥
     * @return byte[] 解密数据
     */
    public static byte[] decryptByPublicKey( byte[] data, byte[] key ) throws Exception {

        //实例化密钥工厂
        KeyFactory keyFactory = KeyFactory.getInstance( KEY_ALGORITHM );
        //初始化公钥
        //密钥材料转换
        X509EncodedKeySpec x509KeySpec = new X509EncodedKeySpec( key );
        //产生公钥
        PublicKey pubKey = keyFactory.generatePublic( x509KeySpec );
        //数据解密
        Cipher cipher = Cipher.getInstance( keyFactory.getAlgorithm() );
        cipher.init( Cipher.DECRYPT_MODE, pubKey );
        return cipher.doFinal( data );
    }

    /**
     * 取得私钥
     *
     * @param keyMap 密钥map
     * @return byte[] 私钥
     */
    public static byte[] getPrivateKey( Map<String, Object> keyMap ) {
        Key key = (Key) keyMap.get( PRIVATE_KEY );
        return key.getEncoded();
    }

    /**
     * 取得公钥
     *
     * @param keyMap 密钥map
     * @return byte[] 公钥
     */
    public static byte[] getPublicKey( Map<String, Object> keyMap ) {
        Key key = (Key) keyMap.get( PUBLIC_KEY );
        return key.getEncoded();
    }
}